Proton-conducting Electrolyte Research Articles

Dynamic release electrolyte design for stable proton batteries.

Aqueous proton batteries (APBs) have recently demonstrated unprecedented advantages in the fields of ultralow temperature and high-power energy applications due to kinetically favorable proton chemistry. Proton acids (e.g. H2SO4, H3PO4) as the common proton-conducting electrolyte, however, seriously corrode electrode materials and current collectors, resulting in limited cycle life of APBs. Here we reported protonated amine as a feasible proton transport mediator and releasing source for APBs based on its dynamic chemical dissociation equilibrium. Free protons in the electrolyte are limited to a quite low level. Consequently, the optimized electrolyte with a nearly neutral pH value significantly suppresses corrosion and broadens material selection option for APBs. The CuFe-TBA electrode exhibited a long cycle performance over 40000 cycles with only ~0.0004% attenuation rate per cycle in the optimized electrolyte. The WO3 and VO2(B) electrode also displayed high cycling stability. Benefiting from enhanced electrode stability in the optimized electrolyte, the resultant CuFe-TBA/WO3 and CuFe-TBA/VO2(B) full batteries display impressive long-term cycling performance with high-capacity retention. Our work presents a proton dynamic-release electrolyte for durable APBs which is highly promising for scalable energy systems.

Preparation of Proton-Conducting Solid Electrolyte Membrane Based on Carboxymethyl Chitosan Complexed with Ammonium Acetate

This research aims to prepare the proton-conducting solid electrolyte membrane based on carboxymethyl chitosan (CMCh) complexed with ammonium acetate (CH3COONH4). The membranes were prepared by using casting solution technique where the various weight percentages of ammonium acetate mixed to CMCh for obtaining optimum condition based on ionic conductivity analysis. Some characterizations were conducted to analysis the functional groups (involving complexation studies), ionic conductivities, mechanical properties, crystallinities, and thermal analysis by using FTIR, EIS, tensile tester, XRD, and TGA. The results showed that the optimum proton conductivity was obtained at the addition of 40% (w/w) CH3COONH4 salt as high as 1.39×10-4 S/cm and a tensile strength of 9.06 MPa. Based on the results, it can be concluded that the optimum condition of the membrane shows good characteristics to be applied as a proton conducting solid electrolyte. Keywords: Ammonium acetate, carboxymethyl chitosan, polymer electrolyte, proton conductivity, proton-conducting membrane

An advanced bifunctional single-element-incorporated ternary perovskite cathode for next-generation fuel cells

Bifunctional perovskite oxides are widely considered to be promising cathode materials for the commercialization of fuel cells, with cobalt-rich variants traditionally preferred. However, challenges such as instability at elevated temperatures and high cost hinder their commercial viability. To address these issues, this study successfully develops a high-performance, cobalt-free ternary cathode material, Ba0.95Pr0.05FeO3-δ (BP5F), by substituting a small amount of Pr into the A-site of the perovskite parent BaFeO3-δ (BF), tailored for bifunctional applications in both solid oxide fuel cells (SOFCs) and protonic ceramic fuel cells (PCFCs). The incorporation of Pr not only optimizes the crystal phase structure but also enhances the oxygen vacancy concentration and triple-conducting capabilities of BP5F. Consequently, this cathode material exhibits remarkable electrocatalytic activity at intermediate-to-low temperatures (ILT, 400–700 °C), with ultra-low area specific resistances of just 0.028 and 0.134 Ω cm2 at 600 °C in symmetrical cells with oxygen ion- and proton-conducting electrolytes, respectively. Correspondingly, in single cells, the peak power densities reach up to 1.528 and 1.135 W cm−2. Furthermore, BP5F demonstrates exceptional long-term durability, operating stably for over 100 h at 600 °C in both SOFC and PCFC single cells. These performance metrics position BP5F among the best-performing ternary perovskite oxides to date. Experimental results combined with theoretical calculations validate the critical role of Pr, establishing BP5F as a highly promising and economically viable bifunctional candidate perovskite cathode, thus providing a significant step towards the commercial development of fuel cell technologies.

A Review of Proton-Conducting Electrolytes for Efficient Low-Temperature Solid Oxide Fuel Cells: Progress, Challenges, and Perspectives

A Review of Proton-Conducting Electrolytes for Efficient Low-Temperature Solid Oxide Fuel Cells: Progress, Challenges, and Perspectives

Y, Yb, and Gd tri-doping on B-site of Ba(Zr, Ce)O3-δ with improved proton conduction performance

Perovskite-type proton conducting electrolytes are garnering significant attention due to its key role in protonic ceramic electrochemical cells (PCEC) and its application in hydrogen sensors (HS) used for metal melt measurements. Developing high proton conduction perovskite materials with good chemical stability is always a worldwide research focus. In this paper, Y, Yb and Gd triple-doping on B-site of BaCeO3-BaZrO3 solid solution were carried out to investigate the effect of gadolinium doping on the performance of protonic conducting electrolytes. BaZr0.1Ce0.7(Y0.5Yb0.5)0.2-xGdxO3-δ (x = 0, 0.1, 0.15 and 0.2), which were also referred as BZCYYbGdx (x = 0, 10, 15 and 20), were synthesized by solid-state reaction at 1600 °C for 10 h. It is found that BZCYYbGd15 has the highest proton conductivity and proton transfer number among the four prepared materials. The proton mobility of BZCYYbGd15 is 4.06 × 10−6 cm2/(Vꞏs) at 800 °C, which increases with an increased temperature. Its proton transfer number is higher than 0.9 at 500 °C under the atmosphere of PH2O = 0.018 atm. A moderate doping of gadolinium increases the temperature threshold for proton conduction. Proton, oxygen vacancy, electron hole and total conductivity activation energies of BZCYYbGd15 under the wet atmosphere are found to be 0.74, 1.58, 1.41 and 0.92 eV, respectively. Furthermore, the chemical stability of pellets is improved after gadolinium doping. This study provides a reference value for future research on high proton conduction electrolytes.

Multivalent metal perovskite YbCoO3 as a novel proton-conducting electrolyte for solid oxide fuel cells

For solid oxide fuel cells, an electrolyte with good stability and high ion conductivity is highly desired but difficult to obtain. Recently, a novel hydrogenation mechanism other than water dissociation have been reported in multivalent metal-based oxides, which provide a new route to increase proton concentration as well as proton conductivity. In this computational study, we propose the multivalent metal perovskite YbCoO3 as a promising proton-conducting electrolyte due to its good thermodynamic and chemical stability, semiconductor characteristics, high-concentration proton incorporation, and low proton migration barrier. Our findings also reveal that charge compensation of the multivalent metal is crucial for the high-concentration proton incorporation. On the other hand, both the shortening of the O-O distance and the Co-H repulsion play key roles in determining the energy barrier to proton migration, where local structural deformations are responsible for facilitating intra- and inter-octahedron proton transfer in YbCoO3. Our results might assist in the development of high-performance proton-conducting electrolytes for advanced solid oxide fuel cells.

Enhanced electrochemical and transport properties of proton-conducting electrolytes through Y and Gd co-doping in BaCe0.6Zr0.2Y0.2-xGdxO3-δ

Enhanced electrochemical and transport properties of proton-conducting electrolytes through Y and Gd co-doping in BaCe0.6Zr0.2Y0.2-xGdxO3-δ

Combining La0.5Sr0.5MnO3-δ cathode with a mixed conductor towards enhanced performance of proton-conducting solid oxide fuel cells

Exploring high-performance cathodes is critical for proton-conducting solid oxide fuel cells (H-SOFCs), as they significantly impact cell performance at intermediate temperatures. Traditional cathodes may also be an attractive option due to their established practicality in practical applications, assuming their cathode catalytic activity can be increased. Traditional Sr-doped LaMnO3 (LSM), one of the most successful cathodes in the community, can only function well at high temperatures, and its performance in H-SOFCs is inadequate. Although using a composite cathode, in which the LSM is coupled with a proton-conducting electrolyte material, typically LSM + BaCe0.7Zr0.1Y0.2O3-δ (BCZY), can improve performance, it remains inferior to many newly produced cathodes, demonstrating insufficient competence. To address this issue, the mixed conductor BSIF, rather than a pure proton conductor, is utilized to pair LSM for the cathode composite. The BSIF mixed conductor has good thermal compatibility with LSM. Furthermore, the H-SOFC with the LSM + BSIF cathode performs better than fuel cells with LSM or BSIF cathodes. An apparent synergistic effect is discovered. The weight ratio of LSM and BSIF in the composite cathode impacts fuel cell performance, with the optimal composition being LSM (50 wt%) and BSIF (50 wt%). First-principles calculations show that the formation of LSM/BSIF alters the electronic structure of the material, increasing cathode ORR activities. The H-SOFC with the LSM (50 wt%) + BSIF (50 wt%) cathode produces a fuel cell output of 1615 mW cm−2 at 700 °C, which is much higher than that of the conventional LSM + BCZY composite cathode, which is only 725 mW cm−2. Furthermore, the LSM + BSIF provides better chemical stability than the traditional LSM + BCZY composite cathode, making LSM + BSIF a high-performing and robust cathode choice for H-SOFCs.

High-Temperature Mechanical–Conductive Behaviors of Proton-Conducting Ceramic Electrolytes in Solid Oxide Fuel Cells

Proton-conducting solid oxide fuel cells (P-SOFCs) are widely studied for their lower working temperatures than oxygen-ion-conducting SOFCs (O-SOFCs). Due to the elevated preparation and operation temperatures varying from 500 °C to 1500 °C, high mechanical stresses can be developed in the electrolytes of SOFCs. The stresses will in turn impact the electrical conductivities, which is often omitted in current studies. In this work, the mechanical–conductive behaviors of Y-doped BaZrO3 (BZY) electrolytes for P-SOFCs under high temperatures are studied through molecular dynamics modeling. The Young’s moduli of BZY in fully hydrated and non-hydrated states are calculated with different Y-doping concentrations and at different temperatures. It is shown that Y doping, oxygen vacancies, and protonic point defects all lead to a decrease in the Young’s moduli of BZY at 773 K. The variations in the conductivities of BZY are then investigated by calculating the diffusion rates of protons in BZY at different triaxial, biaxial, and uniaxial strains from 673 K to 873 K. In all cases, the diffusion rate present a trend of first increasing and then decreasing from compression state to tension state. The variations in elementary affecting factors of proton diffusion, including hydroxide rotation, proton transfer, proton trapping, and proton distribution, are then analyzed in detail under different strains. It is concluded that the influences of strains on these factors collectively determine the changes in proton conductivity.

Enhanced protonic and oxygen-ionic conductivity in Ga-doped Nd2Ce2O7 electrolytes for intermediate-temperature solid oxide fuel cell

Developing mixed oxygen-ion and proton conductors with high ionic conductivity is crucial for advancing intermediate temperature-solid oxide fuel cell (IT-SOFC). In this study, a novel Nd2-xGaxCe2O7 (NGCO, x = 0, 0.05, 0.075, 0.10 and 0.15) ceramic is synthesized by the citric acid-nitrate sol-gel combustion process. The influence of Ga doping on crystal structure, oxygen vacancy, morphology, proton transport characteristic and electrochemical performance of this materials is systematically investigated. It is found that the NGCO exhibits the fluorite-type structure and belongs to space group Fm3¯m. NGCO shows remarkable chemical stability, resisting harmful effects from CO2, water, and wet hydrogen exposure. Adding a small amount of Ga results in high-density ceramics with enlarged grain size and reduced grain boundary density. Nd1.925Ga0.075Ce2O7 (7.5NGCO) displays outstanding conductivities, exceeding Nd2Ce2O7 (NCO) by 271.4% and 248.6% in dry air and wet hydrogen conditions. Further, an anode-supported structure fuel cell with 7.5NGCO electrolyte is constructed and evaluated. The peak power density (PPD) at 700 °C reaches 702 mW/cm2, a 96% enhancement over the fuel cells with NCO electrolyte. These findings indicate that Ga-doped NCO electrolyte holds promise as a proton-conducting electrolyte suitable for IT-SOFC.

Sr-Yb Co-doping of BaCe0.4Zr0.6O3 Proton-Conducting Electrolyte for Solid Oxide Fuel Cells

Sr-Yb Co-doping of BaCe0.4Zr0.6O3 Proton-Conducting Electrolyte for Solid Oxide Fuel Cells

Enriching Nano-Heterointerfaces in Proton Conducting TiO2-SrTiO3@TiO2 Yolk-Shell Electrolyte for Low-Temperature Solid Oxide Fuel Cells.

A challenging task in solid oxide fuel cells (SOFCs) is seeking for an alternative electrolyte, enabling high ionic conduction at relatively low operating temperatures, i.e., 300-600°C. Proton-conducting candidates, in particular, hold a significant promise due to their low transport activation energy to deliver protons. Here, a unique hierarchical TiO2-SrTiO3@TiO2 structure is developed inside an intercalated TiO2-SrTiO3 core as "yolk" decorating densely packed flake TiO2 as shell, creating plentiful nano-heterointerfaces with a continuous TiO2 and SrTiO3 "in-house" interfaces, as well the interfaces between TiO2-SrTiO3 yolk and TiO2 shell. It exhibits a reduced activation energy, down to 0.225eV, and an unexpectedly high proton conductivity at low temperature, e.g., 0.084 S cm-1 at 550°C, confirmed by experimentally H/D isotope method and proton-filtrating membrane measurement. Raman mapping technique identifies the presence of hydrogenated HO─Sr bonds, providing further evidence for proton conduction. And its interfacial conduction is comparatively analyzed with a directly-mixing TiO2-SrTiO3 composite electrolyte. Consequently, a single fuel cell based on the TiO2-SrTiO3@TiO2 heterogeneous electrolyte delivers a good peak power density of 799.7mW cm-2 at 550°C. These findings highlight a dexterous nano-heterointerface design strategy of highly proton-conductive electrolytes at reduced operating temperatures for SOFC technology.

Effect of In and Sc Co-doping on electrochemical performance on bulk and grain boundaries of La1.9In0.05Sc0.05Ce2O7 proton conductors

In this paper, fluorite-type proton conductors La1.9In0.1Ce2O7, La1.9In0.05Sc0.05Ce2O7 and La1.9Sc0.1Ce2O7 (referred to as LCO-I, LCO-IS and LCO-S), were synthesized by the low-cost solid-state reaction method. The formation process and structure of single-doped LCO-I and LCO-S and co-doped LCO-IS were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The electrochemical performance was studied using alternating current electrochemical impedance spectroscopy (EIS). XRD results showed that the synthesized material had a fluorite structure, without any impurity phase. SEM micrographs showed that LCO-I, LCO-S and LCO-IS had a fairly dense grain. EDS analysis confirmed that the elemental composition of LCO-I, LCO-S and LCO-IS was evenly distributed and contained no impurities. LCO-IS exhibited superior conductivity among related materials, and the total conductivity of LCO-IS in oxygen was 9.49 × 10−3 S cm−1 at 800 °C. The effects of co-doping on bulk and grain boundary properties were analyzed using the distribution of relaxation time (DRT). The bulk and grain boundary conductivity of co-doped LCO-IS was higher than that of single-doped LCO-I and LCO-S. LCO-IS showed good proton conductivity. In the temperature range of 300–800 °C, the proton conductivity was 1.35 × 10−6–4.43 × 10−3 S cm−1. For LCO-I and LCO-IS electrolyte supported symmetric cells (Ag ǀ LCO-I (LCO-IS) ǀ Ag), their open circuit voltages were 0.99 V and 0.97 V, respectively, at 700 °C, and the power densities were 8.8 mW cm−2 and 9.34 mW cm−2. This demonstrates the potential of LCO-IS to be used in various devices as a proton-conducting electrolyte.

In situ reconstruction of proton conductive electrolyte from self-assembled perovskite oxide-based nanocomposite for low temperature ceramic fuel cells

In the development of low temperature solid oxide fuel cells (LT-SOFCs), also called ceramic fuel cells, the lack of highly conductive and the high manufacturing cost of dense electrolyte materials severely delay their wide development. In this work, we depart from the classic substitution approach to achieve sufficient ionic conduction (0.01 S cm−2 level at temperature ≥600 °C), a superionic conductive electrolyte material was obtained from a self-assembled hybrid oxide that was derived from the perovskite oxide precursor through alkali metal ion substitution. Moreover, the hybrid oxide was further in-situ reconstructed into a nanocomposite of oxide/carbonate-hydroxide under fuel cell condition. The nanocomposite possesses dominated proton conductivity as verified by the benefited hydration effect, versatile oxygen ionic blocking cell experiment, and concentration cell investigation. Specifically, an outstanding ionic conductivity of 0.185 S cm−1 and an excellent peak power density of 1012 mW cm−2 were demonstrated at 550 °C under an typical H2/air atmosphere. This research offers a rational design strategy to achieve low temperature, high-performance semiconductor-based functional composite electrolytes for efficient and sustainable energy conversion in SOFC technology.

Accelerating the Development of Oxygen Electrodes for Solid Oxide Cells Using Two-Stage Machine Learning

Reversible Solid Oxide Cells (RSOCs) stand out as highly efficient and cost-effective devices for energy storage and conversion. However, the pursuit of high-performance and durable RSOCs is impeded by the lack of efficient and stable oxygen electrodes. The conventional trial-and-error approach used for the development of oxygen electrodes is resources and time-consuming. In this presentation, we introduce a novel "two-stage machine learning" approach designed to expedite the discovery of optimal oxygen electrodes for efficient oxygen reduction/evolution reaction (ORR/OER) in SOCs. In the initial stage, we employed a high-throughput calculation approach to generate four ORR/OER related descriptors (energy above the convex hull, p-band center, d-band center, and vacancy formation energy) for a set of 4455 perovskite oxide candidates. Subsequently, we successfully predicted these descriptors using machine learning techniques based on the fundamental physico-chemical features of the candidates. Moving to the second stage, we measured the polarization resistances - directly related to ORR/OER activity - of 142 oxygen electrodes and employed them as prediction targets. Through our machine learning method, we accurately predicted experimental results based on the fundamental physico-chemical features of the candidate materials. Notably, among the 4455 candidates studied, a specific oxygen electrode material is predicted to exhibit both high activity and stability. When applied to an RSOC based on a proton-conducting electrolyte operated at 600 °C, a high peak power density of >1.5 W cm−2 is demonstrated in the fuel cell mode, and a high current density of >2.5 A cm−2 is achieved at a cell voltage of 1.3 V in the water electrolysis mode while maintaining stable operation for 500 hours.

The effect of Zn-doping on electrical properties, hydration, sintering and chemical resistance of hexagonal perovskite Ba7In6Al2O19

A CO2-stable, easily sintered proton-conducting oxide electrolytes based on solid solution Ba7In6Al2–xZnxO19-0.5x with hexagonal structure has been synthesized for the first time. Within the homogeneity region (0 ≤ x ≤ 0.10), there is an increase in unit cell parameters, cell volumes and free cell volumes. The addition of Zn2+ markedly improved the sinterability of the material. The relative density of the ceramics of the doped samples reached 95 % at lower sintering temperatures than the parent phase. The electrical conductivity was studied using electrochemical impedance spectroscopy. Upon doping the oxygen-ion conductivity increased by 0.25 orders of magnitude at 800 °C. Proton transport was predominant below 500 °C for a wet atmosphere (pH2O = 1.92·10−2 atm). The investigated phases Ba7In6Al2–xZnxO19-0.5x are capable of hydration and incorporate up to 1.45 mol H2O vs 0.41 mol H2O for the parent phase. The studied phases exhibit chemical resistance to CO2 under heat treatment at 600 °C. It was shown that solid solution Ba7In6Al2–xZnxO19-0.5x is a promising electrolyte material for intermediate-temperature fuel cells.

Electrical properties and transport numbers of yttrium and gadolinium co-doped BaCe0.5Zr0.3Y0.2-xGdxO3-δ proton-conducting electrolyte

BaCe0.5Zr0.3Y0.2-xGdxO3-δ (x = 0, 0.05, 0.1) proton-conducting electrolyte materials co-doped with Y (yttrium) and Gd (gadolinium) were successfully synthesized by solid-state reaction method. The influence of Gd concentration on the phase composition, chemical stability, and electrical conductivity of BaCe0.5Zr0.3Y0.2-xGdxO3-δ (BCZYGx, x = 0, 5, and 10) materials were systematically investigated under different atmospheres within the temperature range of 500–800 °C. The BCZYG5 material presents enhanced chemical stability and conductivity in comparison to the pristine BZCY. Electrochemical impedance spectra analysis using the distribution of relaxation times (DRT) and equivalent circuit scheme (ECS) methods revealed that BCZYG5 demonstrates a maximum electrical conductivity of 8.90 × 10−3 S cm−1 at 800 °C under 20 % O2 and 4.51 kPa H2O. The defect equilibrium model was employed to calculate the partial conductivity and transport numbers. The results indicate a decrease in proton transport numbers with rising temperature, while oxygen ion and electron-hole transport numbers increase. The doping of Gd inhibits electron conduction in both the BCZYG5 and BCZYG10, as illustrated by the map of the dominant region of each carrier. This study will serve as a reference for future research.

Proton ions migration in amorphous Nd-alumina oxide based- electrolyte

This study presents a groundbreaking advancement in the field of ceramic fuel cells, namely, solid oxide fuel cells (SOFCs) and proton ceramic fuel cells (PCFCs). In contrast to the prevalent crystalline fluorite oxygen ion-conducting electrolytes and proton-conducting perovskite electrolytes, our study underscores the transformative potential of amorphous oxide material. The Nd-alumina amorphous oxide demonstrates exceptional proton conductivity, reaching 0.16 Scm−1 and an impressive power density of 713 mWcm−2 at 500 °C, thereby surpassing the capabilities of existing crystalline electrolyte materials. Furthermore, this study provides a comprehensive comparison between amorphous Nd-alumina and its crystalline counterparts, thus elucidating the inherent advantages of the amorphous form over traditional crystalline structures. Several characterizations and experimental methods have been introduced for in-depth analysis of proton and oxide ions migration in developed NdAl-Aos electrolytes. However, amorphous Nd-alumina emerges as an alternative component in ceramic fuel cells, propelling an electrolyte technology towards unparalleled performance and paving the way for a sustainable SOFC/PCFC future.

Features of electrical transport and H/D isotope effects in the proton-conducting electrolyte BaCe0.7Zr0.1Y0.1Yb0.1O3-δ

The electrical properties of the proton-conducting electrolyte BaCe0.7Zr0.1Y0.1Yb0.1O3-δ were studied using the 4-probe direct current (DC) method depending on temperature and oxygen partial pressure in the atmospheres, humidified with H2O and D2O. Ionic and electron hole contributions to the electrical conductivity were determined, and the transport numbers of charge carriers were calculated. It is shown that in air conditions BaCe0.7Zr0.1Y0.1Yb0.1O3-δ is a mixed ion-electron hole conductor. The contribution of electron hole conductivity decreases with the decrease of temperature and oxygen partial pressure. A significant isotope H/D effect in the electrical conductivity is observed for all investigated conditions expressed in the decrease in conductivity in D2O-containing atmospheres with the increase of activation energy values. Replacing H2O with D2O leads to decrease in the ion transport numbers and ionic conductivity values, while the electron hole conductivity remains almost the same.

Hydrogen extraction from 0.1 % H2–He mixture: The interplay phenomena of electrode, temperature, and voltage in BZYN & BZCYYb

Hydrogen pumps, crafted from proton-conductive ceramic electrolyte and paired with either oxide or metallic electrodes, have been designed for the extraction of hydrogen isotopes from helium gas mixtures containing 0.1 % hydrogen isotopes, particularly within the context of TES for nuclear fusion reactors. This study presents the electrochemical hydrogen permeation research conducted on the perovskite proton conductor materials BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) and BaZr0.8Y0.16Ni0.04O3-δ (BZYN) under these operational conditions. It was observed that nickel electrodes provided superior performance over SrFe0.8Mo0.2O3-δ (SFM) electrodes in terms of hydrogen extraction efficiency. Hydrogen pumps that integrated BZCYYb as the electrolyte with nickel electrodes showed enhanced efficiency, while those utilizing BZYN as the electrolyte coupled with nickel electrodes demonstrated greater stability. Furthermore, the study explored the voltammetric nonlinearity at low hydrogen concentrations and the dependency of concentration polarization efficiency on both voltage and temperature, aiming to establish optimal conditions that balance stability and efficiency for both types of hydrogen pumps.